a. Field of the Invention
This invention relates to a system and method for generating an electrophysiological map of an object of interest within the body such as the heart. In particular, the invention relates to a system and method that enable derivation of the map without inserting an EP mapping catheter into the body by using electrodes that are placed on an external surface of the body.
b. Background Art
The use of electrophysiological (EP) mapping data in the diagnosis and treatment of tissues within a body is well known. For example, EP maps of heart tissue can be used to guide ablation catheters which are used to convey an electrical stimulus to a region of interest within the heart and create tissue necrosis. Ablation catheters may be used to create necrosis in heart tissue to correct conditions such as atrial arrhythmia (including, but not limited to, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter). Arrhythmias can create a variety of dangerous conditions including irregular heart rates, loss of synchronous atrioventricular contractions and stasis of blood flow which can lead to a variety of ailments and even death. It is believed that the primary cause of arrhythmia is stray electrical signals within the left or right atrium of the heart. The ablation catheter imparts ablative energy (e.g., radiofrequency energy) to the heart tissue to create a lesion in the heart tissue. This lesion disrupts electrical pathways and thereby limits or prevents stray electrical signals that lead to arrhythmia. In addition to guiding ablation catheters, EP maps can also be used to evaluate the effectiveness of ablation therapy.
In a conventional EP mapping system, a catheter is inserted within a vessel located near the surface of a body (e.g., in an artery or vein in the leg, neck, or arm) and maneuvered to a region of interest within the body. Electrodes disposed at one end of the catheter detect changes in electrical potential resulting from the transmission of electrical signals between points on the body. In the EP mapping system sold under the registered trademark “ENSITE” by the assignee of the present invention, St. Jude Medical, Atrial Fibrillation Division, Inc., surface electrode patches are applied in several locations on a body. Electrical signals are transmitted between the patches along orthogonal pathways and one or more electrodes supported on a catheter disposed within the body detect changes in voltage and generate signals that are used to generate an image of a tissue surface
Although existing EP mapping systems function well for their intended purpose, it is desirable to reduce or eliminate the need to insert an EP mapping catheter within the body to obtain EP data. Inserting an EP mapping catheter into the body creates a variety of risks including, for example, potential damage to internal tissues and adverse patient reactions to anesthesia used during the EP mapping procedure. In addition, as with any surgical procedure, insertion of an EP mapping catheter requires significant time and resources on the part of the patient and/or clinician in preparing for the procedure, carrying out the procedure, and in recovery. Furthermore, inserting an EP mapping catheter may cause patient discomfort during and/or following the procedure.
In order to address the issues set forth above, approaches have been developed to obtain EP data for internal body structures such as the heart using electrodes placed on an external body surface. In U.S. Pat. No. 7,016,719, for example, an electrode vest is placed over the patient. An image of the heart such as a fluoroscopic, ultrasound, computed tomography (CT), or magnetic resonance (MR) image is used to define a geometric relationship between the electrodes on the external body surface and the heart. Using this relationship, electrical potentials on the heart surface are then determined in response to potentials measured by the external electrodes. Although the system described in U.S. Pat. No. 7,016,719 eliminates the need for an EP mapping catheter, the accuracy of the system is limited. In particular, the geometric relationship established by the system fails to account for the wide variety of tissues types disposed between the external surface of the body and the heart surface. Different types of tissues within the body have significantly varying impedances. Further, the amount of these tissues will vary along any given pathway from the external body surface to the heart. The geometric relationships advanced in the system described in U.S. Pat. No. 7,016,719 cannot account for this variation in tissue types and amounts.
The inventors herein have recognized a need for a system and method for generating an electrophysiological map that will minimize and/or eliminate one or more of the above-identified deficiencies.